Steel is a high strength material having versatile fabrication capabilities. A wide variety of alloys and processing conditions also allow the properties of steel materials to be optimized for its intended application. These characteristics make steel an excellent choice for a numerous structural applications.
For example, railways and tramways make extensive use of steel materials in the rail systems. Although many advantages are realized by using steel rails, these structures are subjected to significant stresses and failure can result. Further, as ever increasing weights are being freighted at higher speeds and greater frequency, there is an ongoing demand for steel materials having improved properties.
One structural member that experiences particularly high, repetitive stress is the frog, the intersecting point of a railway switch that allows the flanges of wheels moving along one of the rails to pass across the other. The frog supports the wheels over the missing tread surface between the frog throat and the frog point and provides flangeways for aligning the wheels when passing over the switch so that maximum bearing area is preserved. As can be appreciated, these structures are subject to high operational and axial loads and must be very reliable and resistant to failure. Thus, many attempts have been made to produce steel materials that increase the strength and reliability of frogs.
One steel conventionally used to cast frogs is a pearlitic steel, which is known under the tradename UIC 900A. This steel is iron alloyed with 0.60% to 0.80% carbon, up to 0.5% silicon, 0.80% to 1.3% manganese, up to 0.04% phosphor and up to 0.04% sulfur, all by weight. However, this material exhibits relatively low strength and wear resistance and suffers from a short service life. In particular, this steel is subject to the development of blanks, has low notch toughness and susceptible to fracture.
Another prior art material is an austenitic steel, which is known under the tradename 13Mn Super Special. This steel is iron alloyed with 0.60% to 0.80% carbon, 12.50% to 16.50% manganese, up to 0.6% silicon, up to 0.05% phosphor, up to 0.03% sulfur, and 1.80% to 2.20% molybdenum, all by weight. Although this steel offers increased strength, as compared to UIC 900A, its composition makes welding operations with high carbon steels very difficult.
Further, the protocols for ultrasound imaging fault analysis of this material differ from other steels. As a result, the maintenance costs associated with this material are significantly increased. Although improved, the wear resistance of 13Mn Super Special has not been found sufficient to justify the increased maintenance costs.
Yet another prior art steel is known under the tradename Lo8CrNiMo. This alloy comprises 0.11% to 0.15% carbon, 0.50% to 0.80% manganese, up to 0.50% silicon, 1.60% to 2.00% chromium, 2.60% to 3.00% nickel, 0.40% to 0.50% molybdenum, up to 0.003% boron, up to 0.045% aluminum, up to 0.13% vanadium, up to 0.05% titanium, up to 0.012% nitrogen, up to 0.015% phosphor, and up to 0.012% sulfur, all by weight. This steel has improved wear resistance, but is relatively low in strength, and thus is limited to situations where the average operational load is up to 22.5 MT per axle.
It is therefore an object of the present invention to provide a structural member formed from steel alloy having improved strength, wear resistance, weldability and operational service life.
It is a further object of the invention to provide a chrome-nickel-molybdenum steel suitable for frogs.
It is yet another object of the invention to provide a bainitic steel for use with railway and tramway structural members.